The present invention relates to an apparatus for continuously monitoring liquid level conditions in a liquid-vapor separating device.
In the field of separating vapors and liquids from one another, there are many two-phase mixtures which are to be separated from one another such as the separation of steam from water in a boiler and other two-phase mixtures such as natural gas and hydrocarbons. Steam drums are one type of liquid-vapor separating device which are widely used for separating and drying steam.
Steam generated in a subcritical pressure drum type boiler is intimately mixed with large and variable amounts of circulating boiler water. Before the steam leaves the boiler and enters the superheater, practically all of this associated boiler water must be separated from the steam. This separation must be done within a limited space in the steam drum, within a matter of seconds and under a variety of velocity, pressure and other operating conditions. The pressure drop across the steam and water separators must be kept to a minimum so as not to affect the boiler circulation or water level controls.
The drum of a subcritical pressure boiler serves several functions, the first being that of collecting the mixture of water and steam discharged from the boiler circuits. Also, the drum houses equipment to separate the steam from the water and then purify the steam after it has been separated. The drum internals in subcritical pressure boilers not only separate water from steam but also direct the flow of water and steam to establish an optimum distribution of fluids in the boiler during all loads of boiler operation. The internals may consist of baffles which change the direction of flow of a steam and water mixture, impellers and separators which use a spinning action for removing water from steam or moisture coalesces such as screen and corrugated plate final dryers. These devices are used singly or in consort to separate and purify the steam and remove impurities from the steam leaving the boiler drum.
Failure to control the water level in the drum can lead to damage of the boiler. For example, if the water level becomes too low, the drum interior may be heated excessively, resulting in warpage or plastic deformation of the drum. Moreover, an excessive pressure condition in the drum may result. If the water level becomes too high, vapor may exit the drum which is not sufficiently dry for the next following operationxe2x80x94i.e., there will be excessive moisture carryover. If, for example, a next following operation involves the flow of the vapor into the tubes of a superheater, thermal stress damage may occur or, if a next following operation involves flow of the vapor over the blades of a turbine, the insufficiently dry vapor may undesirably corrode the turbine components.
It is known to calculate a variation or imbalance between the flow of vapor or a liquid vapor mixture into a drum (referred to as inlet flow) and the flow of separated vapor from the drum (referred to as outlet flow) and to evaluate this variation or imbalance of the inlet-outlet flow for the purpose of estimating the water level in the drum. It is further known to coordinate the operation of the drum or the boiler or other device which supplies the liquid-vapor mixture to the drum as a function of the estimated water level including, for example, coordinating the operation of the boiler to de-activate or xe2x80x9ctripxe2x80x9d the boiler in the event that it is determined that a water level exists which is below a preestablished minimum. A system is described, for example, in U.S. Pat. No. 4,433,646, for performing such a boiler xe2x80x9ctripxe2x80x9d.
It is also known to monitor the water level in a steam drum by monitoring the water level in a reference receptacle. For example, Japanese Patent Publication 06 27 2804 A2 discloses a reference level which is monitored by a water level transmitter.
In spite of the efforts to provide devices capable of monitoring water level conditions in a liquid-vapor separation drum, as evidenced by the conventional devices mentioned hereinabove, there still exist shortcomings in such conventional devices which render the monitoring of drum water level conditions less than satisfactory. For example, such conventional devices oftentimes are only capable of sensing a minimum and/or a maximum water level in the drum, whereby the absence of any warning of an impending minimum or maximum water level condition forecloses the possibility to undertake a corrective water level adjustment; instead, the sensing of such a minimum or maximum water level typically requires that a boiler trip or other operation interruption be undertaken to prevent damage to the drum. Also, the sensing of the water level in a drum by an indirect method such as by the use of a reference water level undesirably adds to the costs and complexity of the drum operation.
Thus, the need still exists for an apparatus capable of providing information concerning the water level conditions in a liquid-vapor separation drum which could directly sense or monitor the actual water level conditions. Moreover, the need still exists for such an apparatus which could not only sense minimum or maximum water level conditions but could also continuously sense actual water level conditions across a predetermined range of water levels bounded by a minimum water level and a maximum water level.
It is one object of the present invention to provide a vessel condition monitoring apparatus which is capable of providing information concerning the water level conditions in a liquid-vapor separation vessel by directly sensing or monitoring the actual water level conditions in the vessel.
It is another object of the present invention to provide a vessel condition monitoring apparatus which continuously senses actual water level conditions in the vessel being monitored across a predetermined range of water levels bounded by a minimum water level and a maximum water level.
These and other objects of the present invention are provided, in accordance with one aspect of the present invention, by an apparatus for providing information concerning a condition of a vessel such as a steam drum which segregates steam and water from one another, whereby the apparatus includes a first water contact assembly, a signal generator element, and a housing and a conduit for enclosing the signal generator element in a substantially leak proof manner within the vessel space.
In accordance with further details of the one aspect of the present invention, the first water contact assembly is disposable at a first vessel location in the vessel and has a first vibration component operable to vibrate at natural frequencies which vary as a function of a predetermined characteristic of the water at the first vessel location and a first support component for supporting the first water contact assembly in contact with the water at the first vessel location. Also, the signal generator element is operable to generate a signal indicative of a natural frequency of the first vibration component.
In accordance with additional details of the one aspect of the present invention, the vessel condition monitoring apparatus of the present invention includes vessel remote signal receipt means for receiving the signal generated by the first signal generating means at a location outside the vessel enclosed space. Additionally, the vessel condition monitoring apparatus of the present invention includes a signal transmitting element extending between the first signal generating means in the enclosed vessel space and the vessel remote signal receipt means outside the vessel enclosed space. The vessel condition monitoring apparatus of the present invention additionally preferably includes a conduit through which extends the signal transmitting element, the conduit being sealingly connected to the first enclosing means and being substantially leak proof such that the infiltration of water from the enclosed vessel space into the conduit and the first enclosing means is substantially prevented.
The vessel condition monitoring apparatus of the present invention, in accordance with the one aspect of the present invention, monitors the depth of the water. In this connection, the first vibration component preferably includes a tuning fork oriented to vibrate at a natural frequency which varies as a function of the depth of the water in the enclosed vessel space.
In accordance with another aspect of the present invention, there is provided a second water contact assembly disposable at a second vessel location in the vessel spaced from the first vessel location and having a second vibration component operable to vibrate at natural frequencies which vary as a function of a predetermined characteristic of the water at the second vessel location and a second support component for supporting the second water contact assembly in contact with the water at the second vessel location and the signal generator means is operable to generate a signal indicative of at least one natural frequency of the second vibration component of the second water contact assembly.